The present invention relates to a method of designing a curved surface used for curved surface display and curved surface cutting in a CAD/CAM system (Computer Aided Design/Computer Aided Manufacturing System) loaded in a personal computer, an engineering work-station, a numerical control machine tool, or the like.
Conventional curved surface designing methods have generally related to four-sided surfaces, such as a Coons curved surface, a Bezier curved surface, and the like, in which a curved surface is designed with four sides. As a method of designing a three-sided curved surface patch, there is, for example, such a method as described in Fujio Yamaguchi, "Shape Processing Techhology II", The Nikkan Kogyo Shinbun Ltd., Dec. 28, 1982, pp. 61-66.
As a method of designing three-sided, five-sided and six-sided curved surface patches, there is such a method as described in Hiroaki Chiyokura, "Solid Modeling", Kogyo Chosakai Publishing Co., Ltd., Apr. 30, 1985, pp. 109-118.
The former includes a method in which a quadrangular patch is contracted and a method in which a curved surface is designed by three parameters u, v and w. The latter includes a method in which a polygonal patch is formed by plural quadrangular patches (PT1), (PT2), (PT3), (PT4) and (PT5).
In such conventional curved surface designing methods as described above, a quadrangular patch is mainly used, a method related to a three-sided curved surface patch or a five-or-more-sided curved surface patch has an algorithm which is effective only for a three-sided curved surface, or another method is a complicated one in which a polygonal patch is composed of quadrangular patches.